In this gloriously sick splatter classic, creepy old Roberts Blossom plays a fella named Ezra Cobb, but anyone with half a brain knows who he really is: He’s Ed Gein, the pride of Wisconsin. He’s Ed Gein right down to his floppy winter cap. And he’s certainly Ed Gein in his habit of collecting body parts and entrails from the graves of the freshly dead, crafting knick-knacks out of human organs, and lounging around his farmhouse wearing the rotten skin of corpses. 
It’s among the first films to dramatize Ed Gein’s real life. Psycho took parts of the Gein story and juggled ’em around. The Texas Chainsaw Massacre refashioned the Gein legend into a slasher flick about teens who get chased by a cannibal family. Deranged sticks to the fucked-up facts, for the most part, and it’s all the creepier for it. Roberts Blossom’s sicko farmer is the main character here and we follow him from the death of his religious nut mother—the event that pushes mama’s boy Ezra Cobb/Ed Gein over the edge—and on through his bloody exploits.
It’s a solid horror film, but its secret weapon is its dark sense of humor. It’s what makes this movie so entertaining. Ezra Cobb is a hilarious clod and his mother fixation is played for laughs. The comic highlight here though is easily the seance scene in which a lonely widow tries to get Ezra in bed by claiming that it’s a request from her dead husband.
Bob Clark was originally approached to direct, but he reportedly found the material too disturbing. However, Clark did stay on as an uncredited producer and writer Allan Ormsby took over as director with help from actor Jeff Gillen.